i beleave that in the movie, the contents of the breifcase was marsellus'soul, I have been led to beleave this as i have a little bible knowlege, for example, the band-aid on the back of marsellus' head, when the devil extracts a soul from a person's body, he does it from the back of their head, when jules and vincent enter the apartment with the three kids in it, they were possibly there to represent satan's 3 helpers, and when he is looking for the breifcase in the cupboards, he initially looks in the top cupboard, meaning to represent heaven before he is told to look in the cupboard by his feet, representing hell, where marsellus' soul belongs. Also, did you catch the combonation for the breifcase? 666, the number of the devil. And when the kid comes out of the bathroom with the hand-cannon, my views are similar to those of jules, where the bullets were fired at them and were stopped, or redirected by some sort of divine intervention, also there are little things, like where butch rescues marsellus' from the pawn shop after marsellus is raped, he rides out on a motorcycle named 'grace', which may be the name of the bike, or it may be meaning to make a referance to 'the grace of god', which butch rides out of LA (the city of angels) on. I hope this answered some questions to the film. and helped you understand that bit more
